• Tunnel and Underground Space
• /
• v.17 no.3 s.68
• /
• pp.216-224
• /
• 2007

Blasting, using shock and dynamic energy of explosive, is very effective tunnel excavation method. But it had serious problem which is the blast vibration and over-break. In recent study, pre-cracked excavation method using notch hole reduced blast vibration and over-break in tunnel, so we performed study about developing notch bit system for making notch hole. In order to make notch hole effectively we had perform drilling experiments changing length and height of notch and in order to improve speed and precision of drilling we had developed notch bit system which consists of drilling bit, notch bit, adapter and notch guide.

• Tunnel and Underground Space
• /
• v.30 no.4
• /
• pp.404-416
• /
• 2020

An analytical procedure for calculating the failure load of a V-shaped rock notch under two-dimensional stress conditions was developed based on the slip-line plastic analysis method. The key idea utilized in the development is the fact that the α-line, one of the slip-lines, extends from the rock notch surface to the horizontal surface outside the notch when the rock around the notch is in the plastic state, and that there exists an invariant which is constant along the α-line. Since the stress boundary condition of the horizontal surface outside the rock notch is known, it is possible to calculate the normal and shear stresses acting on the rock notch surface by solving the invariant equation. The notch failure load exerted by the wedge was calculated using the calculated stress components for the notch surface. Rock notch failure analysis was performed by applying the developed analytical procedure. The analysis results show that the failure load of the rock notch increases with exponential nonlinearity as the angle of the notch and the friction of the notch surface increase. The analytical procedure developed in this study is expected to have applications to the study of fracture initiation in rocks through wedge-shaped notch formation, calculation of bearing capacity of the rock foundation, and stability analysis of rock slopes and circular tunnels.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.8
• /
• pp.693-701
• /
• 2016

In this study, notch defects are evaluated using fracture mechanics. To understand the effects of notch defects, FE analysis is conducted to predict the limit load and J-integral for middle-cracked and single-edge cracked plates with various sizes of notch under tension and bending. As the radius of the notch increases, the energy release rate also increases, although the limit load remains constant. The values of fracture toughness($J_{IC}$) of SM490A are determined for various notch radii through FE simulation instead of conducting an experiment. As the radius of the notch increases, the energy release rate also increases, together with a more significant increase in fracture toughness. To conclude, as the notch radius increases, the resistance to crack propagation also increases.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1358-1361
• /
• 2003

In this study, intrinsic static/dynamic fracture toughness of Al 7175-T74 are evaluated from the apparent static/dynamic toughness of notched specimen. The notch/crack critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The notch/crack critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, critical notch root radius can be predicted by notch/crack critical average stress fracture model.

• Journal of the Korea Concrete Institute
• /
• v.24 no.5
• /
• pp.525-533
• /
• 2012

In this study, bending tests were performed on beam specimens made of UHPCC with the fiber content range of 0~5 vol% to investigate the contribution of fiber content to first cracking strength and flexural tensile strength. Also, four-point bending tests for unnotched beam as well as three-point bending test for notched beam were performed to estimate the effect of the presence of notch on the strengths. The experiment result showed that the increase in fiber content made linear improvement in the flexural tensile strength; whereas first cracking strength was enhanced only when at least 1 vol% of fibers was incorporated. Comparison of the bending test results with and without notch showed that the notch effect varied with the fiber content. The increase in fiber content diminished the effect of stress concentration on the notch tip, reducing the difference in the strengths. With much higher fiber content, the effect of stress concentration almost disappeared and the defection on cracking plane or the size effect dominated the strengths, consequently resulting in higher strengths in the notched beams than the unnotched ones.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.05a
• /
• pp.160-163
• /
• 2003

In this study, intrinsic dynamic fracture toughness of 17-4PH casting steel is evaluated from the apparent dynamic fracture toughness of notched specimen. Notch radius of notched specimen is manufactured from 0.1mm to 4mm. The results shows that dynamic fracture toughness decreases with decreasing of notch root radius above critical notch roof radius. The true dynamic fracture toughness can be predicted from test results of apparent dynamic fracture toughness measured by using notched specimen.

• Journal of the Society of Naval Architects of Korea
• /
• v.35 no.4
• /
• pp.46-54
• /
• 1998

In this paper, the erect of notch geometries on dynamic stress concentration was investigated by using the dynamic photoelasticity and the drop weight loading system Dynamic stress fields arisen by elastic wave through the loading system around various types of notch geometries were captured by using $10^6/sec$ frame rate Cranz-Shardin camera system with 12 photographic frames. We found that dynamic stress concentrations around the notch tip and comer were highly dependent on the change in notch geometries. The elders of dynamic stress singularity ware determined with respect to varying geometries of notches and we explained dynamic stress concentration in terms of the orders of dynamic stress singularity.

• Polymer(Korea)
• /
• v.36 no.1
• /
• pp.59-64
• /
• 2012

The impact strength of material is considered the most important design factor for small and light products. Impact strength is a unique material property, thus the impact strength should not depend upon the geometry of specimen. However it varies according to specimen thickness, notching method, and notch shape. In this study, the variations of impact strength have been investigated according to thickness, notch shape, and notching method of specimen. Engineering plastics such as PC, ABS and POM have been used in this study. Experimental results showed impact strength increased as thickness decreasesd. PC showed the highest increment of impact strength when the thickness was thin. Fractured section of PC showed brittle fracture behavior when the specimen was thick. However it showed ductile fracture behavior when it was thin. The impact strength of in-mold notched specimen showed higher than that of milling notched specimen. PC showed the highest notch sensitivity among the materials used in this experiment.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.44 no.3
• /
• pp.58-63
• /
• 2007

GPS signal is vulnerable to intentional and unintentional interferences since it has a very weak signal power and its structure is well-known. Among the interference rejecting techniques, the ATF is being generally used as a pre-correlation technique. However, it does not have a design parameter relating to the notch width, resulting in the spectral loss around frequency of the interference. The IIR notch filter has a design parameter relating to the notch width and can generate a sharp notch for the CW interference. In this paper, an adaptive IIR notch filter is proposed and the performance is evaluated using software signal generator and real measurements.

• Aerospace Engineering and Technology
• /
• v.1 no.2
• /
• pp.75-82
• /
• 2002

This paper presents a summary of the input data, requirements and notch prediction analysis for sinusoidal excitation test of a satellite. In the notch prediction analysis, the loads at excitation points and internal loads at the important locations on satellite structure were obtained. After checking of limit loads and margin of safety for each location, the notched sinusoidal test inputs were generated using the results of the notch prediction analysis.